Gravity drop hammers are primarily designed for surface breaking of exposed rock and generally consist of a weight capable of being raised to a height within a housing before release. The weight falls under gravity to strike a surface to be broken, either directly (thus protruding through an aperture in the hammer housing) or indirectly via a striker pin.
The present invention is discussed herein with respect to rock breaking devices produced by the applicant including the devices described in PCT/NZ03/000236 and PCT/NZ03/000237 featuring a drop hammer lock and drive mechanism for a powered drop hammer respectively. U.S. Pat. No. 4,383,363 describes a rock breaking apparatus known as, and herein referred to as the Terminator™ and New Zealand patent application No. 540097 describes a striker pin and drop-weight apparatus designed to be attached to an excavator or the like. The term gravity drop hammer is thus used herein to encompass powered drop hammers in addition to those powered solely by gravity.
In operation of the above-mentioned machines it is often desirable to move or lever rock and other material with the hammer or striker pin. Movement of the material can be achieved by placing the hammer or pin against the material and pushing or pulling with the excavator. However, with existing hammers the coupling between the hammer and excavator, known as the mounting plate, is a substantial distance from the striker pin so the pulling forces at the striker pin are low and difficult to control. This large separation between the striker pin and the mounting plate coupling with the excavator also increases the likelihood of generating high uncontrolled forces that can damage the hammer. Mounting the hammer at a distance from the striker pin thus causes time consuming, inaccurate and inconvenient operation of the hammer for the operator.
A rock breaking apparatus described in the applicant's New Zealand patent application No. 540097 can also perform levering and raking in addition to performing surface breaking tasks of conventional hammers.
Raking refers to using the excavator to pull surface rock horizontally along the ground using the side of the pin. The rock can be loose above the ground surface or be friable enough to be drawn towards the excavator after pressing or driving the point of the pin into the in-situ rock. When raking it is necessary for the hammer/arm assembly to remain locked relative to each other. The linkage geometry to maintain such a locked position requires far greater strength than conventional mounting methods, though ideally the linkage should still utilise standard components.
Levering is a particularly useful action of the rock breaking apparatus afore-mentioned. Levering refers to the driving of the point of the striker pin or hammer into non-friable in-situ rock creating or exploiting a crack. Once the crack is established, the operator can lever the hammer and pin through actuation of one end of the boom attached to the excavator and extract the rock from the ground or widen the cracks further. In such applications it is an important advantage to have the maximum torque and thus leverage available to pry intractable rocks.
Another advantage of being able to lever a powered hammer or breaking device is being able to apply the impact point at positions away from the top surfaces of the material to be broken. This is an important advantage of the applicant's previous inventions described in PCT application numbers PCT/NZ03/000235, PCT/NZ03/000236 and PCT/NZ03/000237. Often the rock requires fine manipulation to correctly position the hammer impact over a seam or weak point. In such scenarios, delivering high power in combination with fine control close to the striker pin provides a significant advantage.
Some existing earth working devices are capable of pivoting to allow the device to operate away from the vertical. Such a device is described in WO98/07952 by Persson. This device comprises pivotable links coupled to a drilling rig to pivot the rig by operation of a hydraulic ram. This allows the rig to be pivoted to drill at an angle away from the vertical. However, the device is unsuited for levering action due to the geometry of the linkage limiting the degree of applicable torque to unfeasibly low levels.
The theoretical maximum lifting capacity of an excavator is the moment resolved about the ends or sides of the tracks without tipping the excavator. The allowable lifting moment is a percentage of the tipping moment. However, not all this moment is available for lifting. The excavator arm and hammer assembly extending from the excavator apply a moment to the excavator which must be subtracted from the maximum lifting moment and is governed by;                a. the distance between the excavator and the drop hammer,        b. the mass of the excavator arm and drop hammer, and        c. any forces applied to the drop hammer or excavator arm.        
Thus by minimising the counterproductive inherent tipping moment created by a)-b) above, the capacity of the excavator to resist any additional moments generated during levering and raking operations without tipping over is increased.
The impact energy of the drop hammer, divided by the mass of the excavator is herein defined as the power-to-weight ratio. A greater power-to-weight ratio implies either more breaking power for a given excavator size or a smaller excavator for a given breaking power. The profitability of a system is thus increased by a higher power-to-weight ratio.
Existing gravity drop hammers are attached to excavators via a wing and mounting plate arrangement attached to the excavator arm. These mounting plates must be custom made for each drop hammer and excavator to ensure the geometrical proportions of the plate are correct. The mounting plate and associated fixings on the drop hammer also add substantial weight to the drop hammer, thereby reducing the power-to-weight ratio and absorbing more moment capacity of any given excavator. The wing and mounting plate also increase the distance from the excavator to the centre of gravity of the drop hammer, which also reduces the power-to-weight ratio and absorbs more lifting moment capacity for a given excavator and arm extension.
In many regions globally, excavation, demolition and quarry operations are restricted from using explosives due to the elevated risks of explosives theft by unauthorized parties including rebels, terrorists and the like. Urban encroachment on quarries and mines has also made the use of explosives difficult and expensive in many regions due to community opposition to ground vibration. Obtaining the necessary permissions or consents from the relevant authorities to use explosives for laying roads, railways and pipelines has also become extremely difficult or impossible to achieve due to the above discussed factors. In such regions, it is thus desirable for a rock breaking machine to also be capable of levering embedded rocks, widening cracks, breaking rock faces and raking without the use of explosives.
It is thus desirable to provide a tool for a carrier such as an excavator, capable of striking a surface to be broken, hammered or compacted about a substantially linear axis and which is also capable of applying a torque and side load to an object substantially laterally to said axis to lever and rake rocks or other material.
It is also desirable to provide a tool that is readily attachable to standard excavator arms, enabling cost to be minimised by permitting different tools/implements to be fitted as required.
It is further desirable for the weight of the attachment mechanism of the tool and the distance between the implement and the excavator arm to be minimised.
It would be a yet further advantage for the implement to enable high forces to be applied about the levering pivot point when the implement is attached to an excavator, without damaging the tool or excavator.
There are many linkage systems and implements designed for attaching to earth working machines including those described in WO96/33315, WO90/03473, JP2000132448, JP2002145911, JP2001257017, JP05034057, JP09364906, JP63125843, JP11344858, DE19702624, EP0887475, EP1013835, EP0325358, EP0386904, EP0818581, U.S. Pat. No. 3,529,740, U.S. Pat. No. 3,743,126, U.S. Pat. No. 4,381,167, U.S. Pat. No. 4,486,141, U.S. Pat. No. 5,405,237, U.S. Pat. No. 5,609,464, U.S. Pat. No. 5,592,762, WO01/016433, WO02/22966, WO2004/016864, WO2004/027162 and WO2004/057114.
However, none of the devices described in these documents achieve the objectives of the present invention, i.e. to                a) provide an implement for a rock working machine or excavator that is capable of striking a surface to be broken, hammered or compacted and that is also capable of pivoting so as to lever and rake rocks or other material.        b) minimise the weight of the attachment mechanism of the implement and/or the distance between the implement and the excavator.        c) provide a means of applying sufficient force to embedded rocks and the like to prise them from the ground by levering the tool about a pivot point when the tool is attached to an excavator.        d) provide fine control of the forces in the striker pin.        
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.